Hereinbelow, the invention is presented in relation with catheter balloons, the problems specific thereto and their functionalities, but it is clearly understood that the composition according to the invention is capable of satisfying the technical requirements of other parts of a catheter, especially the stem.
Cuffed expansion catheters are used in percutaneous transluminal coronary angioplasty (PTCA), which is a process that is widely used for treating coronary disease. In the PTCA procedure, a cuffed expansion catheter is advanced in a patient's coronary artery and the catheter cuff is inflated inside the stenosed region of the patient's artery to open the arterial passage and thus increase the blood flow. Generally, the shape and diameter of the inflated cuff are predetermined and correspond approximately to the original diameter of the lumen of the normally dilated artery, so as to dilate the artery but without further widening its wall. Once the cuff has been deflated, the blood flow in the artery thus dilated then resumes and the expansion catheter may be removed therefrom.
To prevent the restenosis rate and to reinforce the space thus expanded, doctors often implant an intravascular prosthesis, generally known as a stent, inside the artery at the site of the lesion. Stents may also be used for repairing vessels or reinforcing a weakened section of a vessel. Stents are generally placed in the desired position inside a contracted or shrunken coronary artery, by means of a catheter balloon similar to an angioplasty catheter balloon, and widened to a larger diameter by expanding the balloon. The balloon is then deflated to remove the catheter and the stent is positioned in the artery at the thus-expanded site of the lesion.
The expansion catheter balloons of the prior art, generally used in angioplasty procedures, are formed from inelastic polymer materials such as polyvinyl chloride (PVC), polyethylene (PE), polyethylene terephthalate (PET), polyolefinic ionomers, and polyamide (PA). One advantage of these inelastic materials, when they are used in catheter balloons, is that the tensile strength, and consequently the mean breaking pressure, of the balloon is high.
Specifically, catheter balloons must have a high tensile strength so as to exert a sufficient pressure on the stenosed vessel to efficiently open the patient's circulation. Furthermore, a high-tensile balloon may be inflated to high pressures without any risk of the balloon bursting during pressurization. Finally, the wall thickness of a high-strength balloon may be reduced, so as to decrease the profile of the catheter without the risk of bursting. Specifically, there is a direct relationship between the bursting pressure and the tensile stress (see in this respect the article “Medical Device and Diagnostic Industry: New extrusion techniques advance catheter design”, by Byron Flagg (Putnam Plastics), http://www.mddionline.com/article/new-extrusion-techniques-advance-catheter-design).
The drawback of these inelastic materials having the least elasticity is their lack of “compliance”. Specifically, these materials are classified as “non-compliant” materials and “semi-compliant” materials, and especially include PET and polyamide. The non-compliant material shows little expansion in response to increasing levels of inflation pressure. For these non-compliant materials, on account of the limited capacity of the balloon to increase its diameter, the inflated balloon must be sufficiently large so that, once inflated, the balloon has a working diameter that is sufficient to compress the stenosis and open the patient's circulation. However, a large-profile non-compliant balloon may make the catheter difficult to advance in the patient's narrow vascular system since, in an uninflated state, these balloons form flat-shaped wings (like a pancake) which extend radially outward. Consequently, the aim of the present invention is to provide a catheter balloon material that has better compliance. Balloons formed from compliant materials have increased flexibility, which improves the capacity of the probe to follow the patient's sinuous vascular system and to pass through the stenosis, and allows the cuff to be correctly positioned at the site of the stenosis. The flexibility of a balloon is expressed by the flexural modulus of elasticity of the cuff. A relatively flexible (or soft) balloon has a relatively low flexural modulus of elasticity, i.e. below about 1000 MPa.
Other polymer materials, in particular copolymers containing polyamide blocks and polyether blocks (PEBA), are used in the manufacture of catheters to improve their glidant aspect and thus to allow more comfortable insertion into a patient's vessels. PEBAs may also be used for manufacturing catheter balloons, and these materials, which have advantageous properties of high tensile strength, high elongation and low flexural modulus, make it possible partly to satisfy the abovementioned requirements.
The compliance of the PEBA materials currently used is marked by a stress (MPa)—strain (%) curve, the profile of which is characterized by a first “compliant” segment, which is generally linear, and a second “non-compliant” segment (not following a linear strain), separated by a transition segment corresponding to the threshold of the stress-strain curve.
It turns out that PEBA balloons often have a nonuniform wall thickness, which is unacceptable for catheter applications on account of the risks of bursting during their inflation.
The aim of the present invention is thus to provide a process for improving and facilitating the manufacture of PEBA-based balloons or cuffs, so that they have the most uniform possible wall thickness. This property is desirable to limit the risks of bursting during their inflation, whether it be during their manufacture or during their use.
The present invention is directed in particular toward providing “compliant” materials, allowing better control of the uniformity of the wall thickness of the catheter balloon, and thus reducing the amount of rejected balloons. The aim of the present invention is also to manufacture balloons or cuffs with walls that are as thin as possible, making it possible both to use balloon catheters that are as uninvasive as possible during their insertion into vessels, and to improve the safety of use of these balloons by limiting their risk of bursting, while at the same time using less polymer starting material.
The Applicant has now found that a special choice of PEBA, having a particular profile curve, makes it possible to readily control the uniformity of the wall thickness of the balloon during its manufacture. Surprisingly, certain PEBA materials which have a compliance curve whose intermediate segment is as short as possible or even nonexistent between the compliant segment and the non-compliant segment, make it possible to readily manufacture balloons of uniform wall thickness. The term “uniform wall thickness” means a wall that has the same thickness over its entire surface.